Radio shielding means



Nov. 1, 1938. R. T. HURLEY 2,134,946 I RADIO SHIELDING MEANS Filed Nov. 2, 1935 2 Sheets-Sheet l 1N VENTOR.

ATTORNEY.

Nov. l, 1938. R. T. HURLEY RADIO SHIELDING MEANS Filed Nov. 2, 1935 2 Sheets-Sheet 2 IN VENTOR.

ATTORNEY.

Patented Nov. 1, 1938 UNITED STATES PATENT OFFICE Bendix Aviation Corporation,

South Bend,

Ind., a corporation of Delaware Application November 2, 1935, Serial No. 47,963

14 Claims.

This invention relates to electrical apparatus. and more particularly to means for shielding electric circuits such as, forexample, the ignition circuit of a radial aircraft engine.

One of the objects of the present invention is to provide a novel ignition harness for an internal combustion engine whereby electrical radiation from the ignition circuit thereof is substantially eliminated. I

It is well-known that electrical radiations from the high tension oscillating circuits employed in the operation of internal combustion engines interfere with radio reception in the vicinity of said engine, such as in an airplane, and render the reception of signals, course indicating beams, and the. like either impossible or inaccurate. Means have accordingly been heretofore provided for screening the ignition circuits of engines by enclosing the various live parts thereof in metal current conducting casings and connecting the latter to each other and to ground for the purpose of avoiding any substantial radiations. The assemblies or harnesses heretofore provided have not, however, been entirely satisfactory, since the same have not been dependable for long periods of service and the servicing of the same has been inconvenient and difficult, comparatively slight repairs requiring the use of a large number of tools and a considerable amount of time and labor by skilled mechanics. Furthermore, the radio shielding apparatuses heretofore provided which are at all practical have been such as to subject the insulation of the ignition cable to deterioration by gasolinaheat, oil and moisture, and in many instances to abrasion, thusreducing the life and dependability of the circuit as well as the effectiveness of the screen.

It is accordingly another object of the invention to provide a novel ignition harness for screening an internal combustion engine ignition-circuit which is so constructed that the same may be readily and easily installed on and removed from the engine as a unit, said harness being further adapted for installation so that necessary repairs to the circuit or harness can be readily and quickly made without removing the entire harness and without removing or disturbing adjustments of other engine parts.

Still another object of the invention is to provide novel means for effectively screening electrical radiations emanating from a current carrying conductor.

A further object is to provide a novel Joint for connecting the individual parts of radiation screening means for an electrical conductor whereby servicing of the same is rendered easy and convenient and an effective continuous screen is insured.

A still further object is to provide a novel electrical radiation screen for an electrical con- .5

ductor which is flexible, moisture proof and heat resisting and which has a high resistance to penetration by gasoline, oil and the like and a high resistance to abrasion, thus rendering the same durable and dependable.

Another object is to provide a novel harness for screening the electrical radiations ofthe ignition circuit of an internal combustion engine which is simple in construction and of light weight, yet durable, effective and dependable in service.

The above and further objects and novel features of the invention will more fully appear from the following detail description, when taken in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not designed as a definition of the limits of the invention, reference for this latter purpose being primarily had to the appended claims.

In the drawings, wherein like reference characters refer to like parts throughout the several views,

Fig. l is a diagrammatic front view of a radial engine illustrating a portion of the shielding harness comprehended by the present invention;

Fig. ,2 is a perspective view showing. the rear of said engine with the novel harness installed thereon;

Fig. '3 is a perspective view illustrating one type of magneto shield which may be employed in carrying out the present invention;

Fig. 4 is a detail view, with parts broken away, of a manifold ring and connections therefor employed in carrying out the invention;

, Fig. 5 is a partial sectional view, with parts broken away, taken on line 55 of Fig. 4;

Fig. 6 is a section taken on line 6-6 of Fig. 4;

Fig. 7 is an enlarged sectional view of a portion of the wall of the shielding conduit of Fig. 5;

Fig. 8 is an enlarged section taken on line 8-8 of Fig. 6;

Fig.9 is a sectional view, with parts broken away, taken on line 9-9 of Fig. 4; v

Fig. 10 is an end view and transverse section taken on line l0-|0 of Fig. 9;

Fig. 1-1 is a front elevation of one type of spar plug shield whichmay be employed in carrying out the invention; and,

Fig. 12 is a side elevation, partly in section and .permanence of operation.

with parts broken away, of the spark plug shield of Fig. 11.

The live parts of the oscillating circuit of the ignition system of aircraft engines, for example, radiate magnetic lines of force which rise and fall with current oscillations in the high tension circuit and which interfere materially with radio reception in the vicinity of the engine. In order to prevent such interference it becomes necessary to provide a metallic shield about all of said live parts for the purpose of intercepting said lines of force and dissipating the energy thereof in the form of electric current which may be conducted to ground by the shield. If the shielding means is to be satisfactorily effective, there must be no substantial break or opening in the shielding system, and it is accordingly highly desirable that all live wires and current carrying parts be completely surrounded by metal when originally installed and that the same be of such construction and materials as not to be susceptible to too rapid deterioration and frequent failure by reason 'of the elements and other conditions under} which the same are required to operate. Acordingly, the shielding harness of the present invention, in the form illustrated, completely encloses the two independent ignition circuits of a dual ignition radio aircraft engine wherein a set of spark plugs is mounted at the front of the engine cylinders and a second set is mounted at the rear thereof, each set being connected to one of a pair of magnetos secured to the rear of the engine.

The novel ignition harness provided is so constructed as to facilitate the servicing and insure In addition, the length of the cable and weight of the entire unit is minimized, all of which are important considerations, particularly in aircraft engines. As shown, said harness comprises a pair of arcuate manifold tubes or rings [5 and 16 extending over an arc of about 120 and adapted to be secured to the front and rear, respectively, of the engine I! by means of suitable brackets, not shown.

Referring more particularly to the shielding harness of that part of the ignition system which includes the front spark plugs, manifold ring I5 is preferably constituted by a thin, light metal tube, such as copper or bronze, which offers comparatively small resistance to the flow of electric current, and may be plated with nickel, chromium, cadmium or the like, if desired. Said tube, in the embodiment illustrated, is made in two parts, one of which is in the form of a T-joint l8 secured to the remainder of the tube by means of an internally threaded coupling nut l8a adapted to cooperate with threads on tube portion l5. One branch of joint I8 extends rearwardly for connection with a novel flexible manifold conduit I! which is in turn connected in a novel manner to hereinafter appear to a two-part metallic shield 20 supported by and covering the high tension terminals of a magneto 2|. The individual current carrying conductors 22 extend from a terminal of the magneto through manifold conduit l9, manifoldv tube l5 and thence through novelly constructed conduits 23, 23a and spark plug shields 24 to the front plugs of the engine. Conduits 23, 23a are connected to manifold tube l5 and shields 24 in a novel manner to appear hereafter. Conductors 22 may be constituted by standard copper wire insulated with natural rubber, fabric and shellac in a well-known manner.

shielding conduits for conductors, the outer surfaces of which have been constituted by metallic braid or fabric. The former type is not wholly satisfactory since sparks are apt to occur between the engine and metallic braid when the latter rubs against the former, thereby producing a fire hazard. A fabric covering is not practical because the same wears too rapidly, becomes oil soaked, and is apt to take fire at engine temperatures. Furthermore, oil, gasoline and moisture penetrate the fabric and seep through the woven metallic shielding and deteriorate the rubber and shellac employed on the current carrying conductors.

Novel flexible tubing is accordingly provided for shielding the conductors between magneto shield 20 and manifold tube [5 and between the latter and spark plug shields 24, which tubing is not subject to the hazard of sparking and has a high resistance to penetration and deterioration by gasoline, oil, moisture, heat and abrasion. One form of the novel tubing is constituted by manifold conduit N which is adapted to shield a plurality of conductors 22 and comprises a braided metallic tube 25, such as phosphor bronze fiat braid, surrounded by a second braided tube 26 of smaller tinned copper wire. The former assists the latter in shielding the current carrying conductors and gives sufiicient rigidity to the conduit to prevent excessive twisting and vibration thereof. Surrounding said metallic tubes and in intimate contact therewith is a covering 21 of synthetic rubber, which is not materially affected by gasoline, oils and other solvents of natural rubber which is employed for insulation on conductors 22. Said covering also has a high resistance to heat, moisture and weather elements and is tough enough to resist abrasion brought about by movement and vibration of the conduit in contact with the engine by reason of wind currents and other causes.

By way of example, one suitable composition of synthetic rubber which may be employed in making covering 21 comprises about of chloroprene as a base, the chemical formula of which is 1 of zinc oxide, 10% of magnesium oxide, 5% of wood resin, and 40% of soft carbonblack. The composition made in accordance with this typical formula may be extruded onto braided wire tubes 25 and 26, thus causing the same to fill the spaces between the strands of wire forming said tubes. Additional rigidity and resistance to twisting movements is thus given to the entire conduit without impairing the longitudinal flexibility thereof, and relative movement of tubes 25 and 26 is obviated.

Another form of the novel shielding conduit provided by this invention is illustrated in Fig. 8 wherein conduit 23 is shown as comprising a wire braided tube 28 having a covering 29 of synthetic rubber of the character above described extruded thereon. In order to give the conduit rigidity, to prevent crushing the latter and to facilitate the insertion of current carrying conductors 22, conduits 23, 23a also include a coil spring 30 within braided tube 28, said spring being under torsional compression and exerting a radial pressure "against the inner walls of said braided tube.

As noted above, the present invention comprehends the use of a plurality of metallic manifold tubes 15 and I 6 in lieu of the single tube with covering 21.

heretofore used in devices of this character and mounted on the rear of the engine, the arcuate length of said tubes-being materially reduced for the purpose of reducing the weight of the harness and facilitating installation and servicing thereof. To further facilitate installation and servicing, novel connecting means are provided in combination with the shielding tubes and conduits whereby the harness may be readily disassembled after installation without interfering with the engine parts and without removing the entire shielding unit and whereby dust and moisture are excluded therefrom. The ends of the shielding conduits and novelly constructed to constitute part of the coupling means and to insure good electrical connections between the several parts of the shielding harness. As shown in connection with conduit I9, said coupling means comprise a pair of flanged metallic ferrules 3i and 32, Fig. 5, the former ofwhich has a tubular portion extending into the conduit and the latter a tubular portion which extends outside of the conduit in intimate contact The flanges on said ferrules extend radially and outwardly in' overlapping relation and the end portions of braided tubes and 26 which extend beyond covering 21 are flared outwardly between said flanges. Said flared portions and flanges are secured together by suitable means such as solder, thus forming a conduit with a clean, as distinguished from a ragged end, and insuring an effective electrical connection. A pair of internally threaded coupling nuts 33 having inturned flanges 34 engaging the flange of ferrule 32 are adapted to cooperate with threads on a branch of T joint l8 and an extended portion of magneto shield 2d to complete the shielding means between the magneto and the manifold tube. Upon screwing coupling nuts 33 tightly into position, the flange of ferrule 3! will be held in firm contact with joint'id or shield 20, as the case may be, thereby forming 'a tight joint and sure electrical connection between the shielding parts.

' A modified coupling is shown for connecting conduits 23 to manifold tube l5 wherein the inner ends of the three conduits which are shown connected to said tube intermediate the ends of the latter are provided with a pair of flanged ferrules 3i: and 36 (Fig. 8) which have tubular portions that extend inside of spring and outside of covering 29, respectively. The flanges on said ferrules overlap and have'the flared end of tube 28 soldered or otherwise suitably secured therebetween. An externally threaded coupling nut 3T is adapted to threadedly engage a nipple 38 which may be permanently secured, as'by means of silver brazing, over an opening in the wall of manifold tube l5. Nut 31 is adapted to engage the flange of ferrule 36 and press the flange of ferrule against the plane surface of an internal flange 39 on nipple 38, thereby forming a tight joint and electrical connection. An

interally threaded coupling-nut 40 (Fig. 12) hav--' ing an internal lip 4| for engaging the flange of ferrule 36 maybe employed for connecting the outer end of conduits 23 to spark plug shields 24.

In the illustrated embodiment of the inven-' tion, three of the current carrying conductors 22 are led out from each end of manifold tube I5, l8 through shielding conduits 23a to the individual spark plug shields 24. Conduits 2311 are similar in construction to conduits 23, and the outer ends thereof are provided with similar coupling means for connection to said spark plug shields. The inner endscf conduits 23a extend through a triangular-like coupling member or ferrule 42 (Figs. 9 and 10.) having three passages therethrough, the inner walls of which are closely engaged by .the synthetic rubber covering 29 of conduits 23a. Braided metallic tubes 28 and springs 30 of said conduits extend beyond the ends of covering 29, are flared outwardly over the inner face of ferrule 42, and are secured thereto. The securing means is preferably constituted by soft soldering in order to permit the renewal of one of the conduits 23a without destroying the entire three-way connection. A circular flange 43 is provided on the inner end of ferrule 42, which is adapted to be held in electrical engagement with a threaded collar 44 brazed to the end of manifold tube ill by means of an internally threaded coupling nut 45 having an inwardly extending lip 46 engaging the outer face of flange 43.

One type of spark plug shield which may be employed in carrying out the invention comprises a cup-shaped body portion 41 adapted to be removably secured to a spark plug 48 by means of a pair of collars 49 and 56 having coacting flanges, the former of which has threaded engagement with an opening in the bottom of body 21 and the latter a like engagement with the metallic body of spark plug 48. An opening at the top of body 41 is covered by a metallic plate 56 and a plurality of layers of mica insulation 52, which plate and layers are held in engagement with the edges of said opening by a flanged ring 53, said ring being secured to the body by peeping the lower edge of the flange thereof over an annular head on body M. For the purpose of liberating ozone which. will be generated within body l'l during engine operation and at the same time avoiding entrance of dirt and moisture, a channel 5c is formed around said body beneath ring 53 and has small alternate openings 55 and into body-4T and to atmosphere, respectively. Threaded into an opening in the side of body is a short tubular member 58 to which a shielded conduit 23 or 23a is adapted to be connected by coupling nut W in the manner above described.

The means for establishing an electrical connection between conductor 22, which extends through conduit 23, and spark plug electrode 59, are preferably constituted by a pin til, an enlarged head portion of which is slidably mounted in a metallic cylinder 6i, the pin being normally held in engagement with electrode 59 by a spring 62 within said cylinder. The inner end of the wire of conductor 22 is flared outwardly and soli dered to a metallic Washer 83 molded into an insulating spool 64. The inner end ofcylinder Si is held in engagement with the flared end of the wire of conductor 22 by an expandible lock spring 65 adapted to coact with an internalgroove in spool M. The movement of said spool in body 41 is limited by a shoulder thereon which v which it is to beadapted. The manifold conduit connecting manifold tube IE to the shield on magneto 2la is of course much shorter than conduit I9, but of the same construction.

There is thus provided a novel radio shielding harness for the high tension shielding circuit of an internal combustion engine whereby electrical radiations and consequent interference with radio reception in the vicinity of the engine are eliminated. Novel shielding means for a current carrying conductor are also provided, which means are so constructed as to offer high resistance to deteriorating causes and agencies present in the operation of an internal combustion engine, thus increasing the life of the harness and decreasing the possibility of failure thereof. Said means are also so constructed as to be readily installed and serviced in the fleld as well as in the shop.

Additionally, there is provided a novel ignition harness for the ignition system of a dual ignition engine wherein each ignition circuit is independently shielded so that in the event of damage to the shield of one circuit the other circuit may be employed singly for operating the engine without any interruption of satisfactory radio reception. The invention also comprehends a novel harness wherein a single shielding conduit is passed between the,hot cylinders of the engine instead of nine conduits, as has been the practice in similar devices heretofore provided, said single conduit being so constructed as to withstand for long periods of time the intense heat, the action of gas, oil and other moistures, and the wearing tendencies to which it is subjected.

Although onlyone embodiment of the invention has been illustrated and described, it is to be expressly understood that the same is not limited thereto but that various changes may be made. For example, manifold tubes l5 and i8 may, if desired, be further divided into pairs on some types of engines to increase the facility with which the same may be serviced. Many other changes may also be made in the design and arrangement of parts illustrated, as will now be apparent to those skilled in the art, without departing from the spirit and scope of the invention. Reference will accordingly be had primarily to the appended claims for a deflnition of the limits of the invention.

What is claimed is:

1. A radio shield for an electric current carrying conductor comprising a flexible metallic tube, a synthetic rubber covering on said tube, and a metallic ferrule at each'end of said tube surrounding said cover, the ends ofsaid tube being electrically connected to said ferrules.

2. A radio shielding conduit for an electric current carrying conductor comprising a flexible metallic tube, a synthetic rubber covering on said tube, a metallic ferrule at each end of said tube surrounding said cover, the ends of said'tube being electrically connected to said ferrules, and a metallic spring under torsional compression within said metallic tube and exerting a radial pressure against the walls thereof.

3. A radio shield for an electrical conductor comprising a flexible metallic tube having a flared end portion, a covering of synthetic rubber for said tube, a metallicferrule surrounding said covering adjacent anend thereof, a metallic spmg inside of said tube, and a ferrule extending into said tube interiorly of said spring, said ferrules having overlapping exterior flanges thereon with the flared end of said metallic tube extending between said flanges in electrical contact therewith.

4. An electrical radiation screen for an electric current carrying conductor comprising a flexible metallic tube, a covering of synthetic rubber on said tube, a metallic ferrule surrounding said cover adjacent an end of said tube, said ferrule having an exterior annular flange at the outer end thereof, and means for electrically connecting the end of said metallic tube to said flange.

5. An electrical radiation screen for an electric current carrying conductor comprising a flexible metallic tube, a. covering of synthetic rubber therefor, a metallic ferrule at an end thereof surrounding said covering and electrically connected to said metallic tube, and a coiled metallic spring under torsional compression within said flexible tube.

6. A radio shield for an electrical conductor comprising a loosely braided wire tube, a comparatively closely braided wire tube surrounding said flrst tube, and a cover of synthetic rubber extruded onto said tubes to surround the same and fill the spaces between the strands thereof.

7. In apparatus of the character described, a

metallic tube having a threaded collar on an end thereof, a flanged ferrule having a plurality of longitudinal passages therethrough, a flexible metallic conduit extending into each of said passages and secured to said ferrule, and a coupling nut adapted to threadedly engage said collar and having an internal flange adapted to engage the flange on said ferrule to hold the latter in contact with said collar. 1

8. In apparatus of the class described, a metallic tube having a threaded portion at an end thereof, a coupling member having a plurality of passages therethrough and a flange adjacent one end thereof, a flexible metallic conduit extending through each of said passages and secured to said member, a synthetic rubber covering on each of said conduits engaging the walls of said passages, and a coupling nut adapted to cooperate with said flange and the threaded portion of said tube to secure said member and tube together and establish an electrical contact therebetween.

9. A radio shield for an electrical conductorcomprising a braided wire tube, a covering 'of synthetic rubber extruded onto said tube to surround the same and flll the spaces between the strands thereof, and a metallic spring within said tube engaging the inner walls thereof.

10. In apparatus of the class described, a metallic tube having an opening in the wall thereof, a flanged nipple covering said opening and electrically secured to said tube, a flexible metallic conduit, 9. covering of synthetic rubber on said conduit, a ferrule on an end of said conduit having a flange, a flared end of said metallic conduit being in electrical contact with said flange, and a coupling nut threadedly engaging said nipple and adapted to hold said flange and flared end against said-nipple whereby a tight Joint is formed and said tube and conduit are held in electrical contact. Y

11. In a radio shielding ignition harness for an internal combustion engine, a substantially rigid metallic conduit, an internally threaded nipple extending outwardly from said conduit, an internal flange on said nipple having a plane face, a flexible metallic tube, a ferrule having an external flange surrounding said tube, and a coupling nut threadedly engaging said nipple to press a flared end of said flexible tube between said flanges whereby a tight joint and electrical contact is established between said conduit and tube.

12. In a radio shielding ignition harness for an internal combustion engine, a substantially rigid metallic conduit, an internally threaded nipple extending outwardly from said conduit, an internal flange on said nipple having a plane face, a flexible metallic tube, a covering of synthetic rubber on said tube, a coil spring in said tube, a flanged ferrule surrounding the covering adjacent an end thereof, a flanged ferrule extending interiorly of said spring, the flared end of said flexible tube extending between the flanges on said ferrules, and a coupling nut' threadedly engaging said nipple to clamp said ferrule flanges and flared portion between said nut and the plane face of said nipple flange.

13. An electrical radiation screen for an electric current carrying conductor comprising a flexible metallic tube, a metallic ferrule surrounding said tube adjacent an end thereof, a metallic spring inside of said tube, and a ferrule extending into said tube'interiorly of said spring, said ferrules having overlapping exterior flanges thereon that have electrical contact with the end of said metallic tube.

14. An electrical radiation screen for an electric current carrying conductor comprising a flexible metallic tube, a coiled metallic spring inside of said tube, and a metallic ferrule extending into said tube interiorly of said spring, said ferrule having an external flange electrically connected to said tube.

ROY T. HURLEY. 

